Studying the efficiency of financial assets is important because, if they are not efficient, this means that investors have some capacity to predict the behavior of those assets. In this paper, we use detrended fluctuation analysis to assess the efficiency of the three most valuable American companies, which, curiously, all happen to be from the same economic sector: Apple, Alphabet, and Microsoft. The results point to the efficiency of Apple's shares and to similar results regarding Alphabet. Only Microsoft shares show evidence of deviations from efficiency. Our results also suggest that moments of crisis could have an impact on the efficiency pattern of shares. (original abstract)